The invention relates to a semiconductor laser having a semiconductor body comprising at least a first passive semiconductor layer of the first conductivity type, an active semiconductor layer disposed thereon and a second passive semiconductor layer of the second opposite conductivity type disposed on the active layer. A pn junction being present between the first and the second passive layer and a groove is provided on the side of the second passive layer in the surface of the semiconductor body, which groove extends at most over only part of the thickness of the second passive layer. Upon application of a voltage in the forward direction across the pn junction, coherent electromagnetic radiation can be produced in a strip-shaped part of the active layer lying below the groove and situated between two reflecting side faces of the semiconductor body substantially at right angles thereto, for which radiation the passive layers have a lower refractive index than the active layer.
The invention also relates to a method of manufacturing the semiconductor laser.
A semiconductor laser of the kind described is known from the British Patent Application No. 2021307, laid open for public inspection.
In semiconductor lasers in which radiation is produced in a strip-shaped active region, one of the main problems is that an efficient heat dissipation from the strip-shaped region must be ensured. For this purpose, a region of very low heat resistance must be present between the active strip-shaped region situated at a certain depth under the surface of the crystal and a heat sink or cooling plate. In fact, an excessively high temperature of the active region leads to an increase of the threshold current and to other disadvantageous effects on the laser action.
Another main problem is that so-called self-pulsations are produced. These instabilities ("kinks") in the radiation-versus-current characteristic are particularly disadvantageous when the laser is used in optical telecommunication systems.
These self-pulsations are suppressed to a considerable extent in a laser structure as described in the aforementioned British Application. In this known laser structure, the semiconductor body is composed of layers of gallium arsenide and gallium aluminum arsenide, while a semiconductor top layer is formed on the second passive layer and a zinc diffusion is effected in the groove up to a certain distance from the active layer. In order to limit the current to the active strip-shaped region, the top layer is of the first conductivity type, opposite to that of the second passive layer, which necessitates an adaptation with respect to the layer structure generally used for double hetero-junction lasers (DH-lasers). This known semiconductor laser must be soldered on a cooling plate at the side on which the groove is provided, in which event the solder must fill the groove completely in order to ensure a good heat transfer. Due to inclusions, in particular gas bubbles, however, the latter is realized insufficiently in many cases, even with special measures. This directly influences the laser characteristic.